The most effective method of ensuring the success of a disinfection or sterilization procedure is consistent adherence to an established, written protocol for cleaning and disinfection or sterilization by specifically trained health-care workers. Before establishing such a protocol or “institutional policy”, a number of basic variables must be considered. These include: The relative infection risks inherent to the instrument, the medical procedure, or the patient, The relative resistance levels of a variety of microorganisms, The comparative powers of a variety of germicidal chemicals, and A number of procedural factors that can influence the effectiveness of germicidal procedures. Microorganisms vary widely in their resistance levels to a given liquid chemical germicide, and these resistance levels can vary even within the same general group or genus. The generic type of chemical germicide, the appropriate concentration, and the appropriate exposure time during a germicidal regimen are all pertinent and interrelated considerations, but are currently among the most confusing choices to be made by the health-care worker. A wide variety of brand-name products promoted for use in reprocessing medical instruments is available. Some have the same basic active ingredient as others but with different additives, supposedly to increase the efficiency or stability of the product. The importance of establishing consistently appropriate and reproducible laboratory test methods to evaluate and compare the germicidal capabilities of liquid chemical agents cannot be overstated.